arm64: force CONFIG_SMP=y and remove redundant #ifdefs

Nobody seems to be producing !SMP systems anymore, so this is just
becoming a source of kernel bugs, particularly if people want to use
coherent DMA with non-shared pages.

This patch forces CONFIG_SMP=y for arm64, removing a modest amount of
code in the process.

Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/include/asm/ptrace.h

@@ -183,11 +183,7 @@ static inline int valid_user_regs(struct user_pt_regs *regs)
 
 #define instruction_pointer(regs)	((unsigned long)(regs)->pc)
 
-#ifdef CONFIG_SMP
 extern unsigned long profile_pc(struct pt_regs *regs);
-#else
-#define profile_pc(regs) instruction_pointer(regs)
-#endif
 
 #endif /* __ASSEMBLY__ */
 #endif